1. Field of the Invention
The present invention relates to thin film transistors and, particularly, to a carbon nanotube based thin film transistor.
2. Discussion of Related Art
A typical thin film transistor (TFT) is made of a substrate, a gate electrode, an insulation layer, a drain electrode, a source electrode, and a semiconducting layer. The thin film transistor performs a switching operation by modulating an amount of carriers accumulated in an interface between the insulation layer and the semiconducting layer from an accumulation state to a depletion state, with applied voltage to the gate electrode, to change an amount of the current passing between the drain electrode and the source electrode.
In prior art, the material of the semiconducting layer is amorphous silicone (a-Si), poly-silicone (p-Si), or organic semiconducting material. The carrier mobility of an a-Si TFT is relatively lower than a p-Si TFT. However, the method for making the p-Si TFT is complicated and has a high cost. The organic TFT is flexible but has low carrier mobility.
Carbon nanotubes (CNTs) are a novel carbonaceous material and received a great deal of interest since the early 1990s. Carbon nanotubes have interesting and potentially useful heat conducting, electrical conducting, and mechanical properties. Further, there are two kinds of carbon nanotubes: metallic carbon nanotubes and semiconducting carbon nanotubes determined by the arrangement of the carbon atoms therein. The carrier mobility of semiconducting carbon nanotubes along a length direction thereof can reach about 1000 to 1500 cm2V−1s−1. Thus, in prior art, a TFT adopting carbon nanotubes as a semiconducting layer has been produced. The carbon nanotubes in the conventional TFT are distributed disorderly to form a disordered carbon nanotube layer or perpendicular to the substrate to form a carbon nanotube array.
However, in the disordered carbon nanotube layer, the carbon nanotubes are arranged disorderly. The paths in the disordered carbon nanotube layer for carriers to travel are relatively long. Thus, the carrier mobility of the disordered carbon nanotube layer is relatively low. Further, the disordered carbon nanotube layer is formed by printing a mixture of a solvent with the carbon nanotubes dispersed therein on the substrate. The carbon nanotubes in the disordered carbon nanotube layer are joined or combined to each other by an adhesive agent. Thus, the disordered carbon nanotube layer is a loose structure and not suitable for being used in a flexible TFT.
In the carbon nanotube array, the carbon nanotubes are perpendicular to the substrate. However, the carbon nanotubes have good carrier mobility along the length direction thereof. Thus, the carrier mobility of the carbon nanotube array along a direction parallel to the substrate is relatively low.
Therefore, the carrier mobility of the two kinds of carbon nanotube layers are both relatively low, and the property of the high carrier mobility of the carbon nanotubes are not effectively used. Further, the carbon nanotube layers are both inflexible.
What is needed, therefore, is a TFT in which the above problems are eliminated or at least alleviated.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present thin film transistor, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.